A permanent magnet type rotating electrical machine that is equipped with a rotor where a permanent magnet s embedded as a rotating electrical machine is known.
As shown in FIG. 8A and FIG. 8B, a rotor 100 of a permanent magnet type rotating electrical machine is formed by inserting permanent magnets 103 into slots 102 formed in a rotor core 101.
In the permanent magnet 103, when a corner part that is most distant from a perimeter surface 101a, which is a peripheral surface in the stator side of the rotor core 101 is defined as a first corner part 103a, and a corner part in a position that faces the first corner part 103a is defined as a second corner part 103b, there is a possibility that the second corner part 103b becomes demagnetized permanently because the second corner part 103b is exposed to a strong demagnetizing field originating from the stator side.
Here, the demagnetizing field is defined as a magnetic field received from an exterior in a direction opposite to a magnetization direction of the permanent magnet 103.
That is, as shown in FIG. 8B, when the magnetic flux from the stator side short-cuts to the rotor core 101 near the first corner part 103a through the rotor core 101 near the second corner part 103b, there is a possibility that the demagnetizing field concentrates on the second corner part 103b may arise.
A technology protecting a permanent magnet against demagnetization by increasing a thickness in the magnetization direction in a part where it exposed to the demagnetizing field of the permanent magnet is disclosed in Japanese Patent Application Laid-Open Publication No. 2008-283823.
However, the thickness of the permanent magnet in the magnetization direction must be increased as a peak intensity of the demagnetizing field increases in order to prevent permanent demagnetization, and the problem that the amount of magnets increases arises.